$J/\psi$ and $\psi(2S)$ production at forward rapidity in $p$+$p$ collisions at $\sqrt{s}=510$ GeV

TL;DR

This paper reports measurements of $J/\psi$ and $\psi(2S)$ production at forward rapidity in proton-proton collisions at 510 GeV, comparing results with theoretical models and previous data to understand quarkonium production mechanisms.

Contribution

First measurement of $J/\psi$ and $\psi(2S)$ production at 510 GeV in forward rapidity, with comparisons to QCD calculations and previous experiments.

Findings

Total $J/\psi$ cross section measured as 54.3 nb with uncertainties.

Theoretical models overestimate low-$p_T$ data and underestimate at higher $p_T$.

Results are consistent with previous measurements at different energies within uncertainties.

Abstract

The PHENIX experiment at the Relativistic Heavy Ion Collider has measured the differential cross section, mean transverse momentum, mean transverse momentum squared of inclusive $J/\psi$ and cross-section ratio of $\psi(2S)$ to $J/\psi$ at forward rapidity in \pp collisions at \sqrts = 510 GeV via the dimuon decay channel. Comparison is made to inclusive $J/\psi$ cross sections measured at \sqrts = 200 GeV and 2.76--13 TeV. The result is also compared to leading-order nonrelativistic QCD calculations coupled to a color-glass-condensate description of the low-$x$ gluons in the proton at low transverse momentum ($p_T$) and to next-to-leading order nonrelativistic QCD calculations for the rest of the $p_T$ range. These calculations overestimate the data at low $p_T$. While consistent with the data within uncertainties above $\approx3$ GeV/$c$, the calculations are systematically below the data. The total cross section times the branching ratio is BR $d\sigma^{J/\psi}_{pp}/dy (1.2<|y|<2.2, 0<p_T<10~\mbox{GeV/$c$}) =$ 54.3 $\pm$ 0.5 (stat) $\pm$ 5.5 (syst) nb.